Commentary on Proposition XIII.4

Back to Proposition XIII.4.

[Folio 0452 | p. 448]

Here, as in the preceding propositions, the results are proved de novo by the method of Book II., without reference to that Book. Otherwise the proof might have been shorter.

For, by II. 7,

(sq. on AB) + (sq. on BC) = 2 (rect. AB, BC) + (sq. on AC) = 3 (sq. on AC).